// Copyright (c) 2021 Lars Pontoppidan. All rights reserved.
// Use of this source code is governed by an MIT license
// that can be found in the LICENSE file.
module parser

import toml.ast
import toml.checker
import toml.util
import toml.token
import toml.scanner

// Parser contains the necessary fields for keeping the state of the parsing process.
pub struct Parser {
pub:
	config Config
mut:
	scanner   &scanner.Scanner
	prev_tok  token.Token
	tok       token.Token
	peek_tok  token.Token
	tokens    []token.Token // To be able to peek more than one token ahead.
	skip_next bool
	// The root map (map is called table in TOML world)
	root_map     map[string]ast.Value
	root_map_key string
	// Array of Tables state
	last_aot       string
	last_aot_index int
	// Root of the tree
	ast_root &ast.Root = &ast.Root{}
}

// Config is used to configure a Parser instance.
// `run_checks` is used to en- or disable running of the strict `checker.Checker` type checks.
pub struct Config {
pub:
	scanner    &scanner.Scanner
	run_checks bool = true
}

// new_parser returns a new, stack allocated, `Parser`.
pub fn new_parser(config Config) Parser {
	return Parser{
		config: config
		scanner: config.scanner
	}
}

// init initializes the parser.
pub fn (mut p Parser) init() ? {
	p.root_map = map[string]ast.Value{}
	p.tokens << p.scanner.scan() ?
	p.next() ?
}

// run_checker validates the parsed `ast.Value` nodes in the
// the generated AST.
fn (mut p Parser) run_checker() ? {
	if p.config.run_checks {
		chckr := checker.Checker{
			scanner: p.scanner
		}
		chckr.check(p.root_map) ?
		for comment in p.ast_root.comments {
			chckr.check_comment(comment) ?
		}
	}
}

// parse starts parsing the input and returns the root
// of the generated AST.
pub fn (mut p Parser) parse() ?&ast.Root {
	p.init() ?
	p.root_table() ?
	p.run_checker() ?
	p.ast_root.table = p.root_map
	return p.ast_root
}

// next forwards the parser to the next token.
fn (mut p Parser) next() ? {
	p.prev_tok = p.tok
	p.tok = p.peek_tok
	if p.tokens.len > 0 {
		p.peek_tok = p.tokens.pop()
		p.peek(1) ?
	} else {
		p.peek(1) ?
		p.peek_tok = p.tokens.pop()
	}
}

// peek peeks forward `n` tokens.
// peek returns `.unknown` if it can not peek ahead long enough.
fn (mut p Parser) peek(n int) ?token.Token {
	if n < 0 {
		return error(@MOD + '.' + @STRUCT + '.' + @FN + ' peeking backwards is not supported.')
	}
	if n == 0 {
		return p.peek_tok
	} else {
		// n >= 1
		if n <= p.tokens.len {
			return p.tokens[n - 1]
		} else {
			mut token := token.Token{}
			mut count := n - p.tokens.len
			util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'buffering $count tokens...')
			for token.kind != .eof && count != 0 {
				token = p.scanner.scan() ?
				p.tokens << token
				count--
			}
			return token
		}
	}
}

// check forwards the parser to the next token if the current
// token's `Kind` is equal that of `check_token`.
fn (mut p Parser) check(check_token token.Kind) ? {
	if p.tok.kind == check_token {
		p.next() ?
	} else {
		return error(@MOD + '.' + @STRUCT + '.' + @FN +
			' expected token "$check_token" but found "$p.tok.kind" in this (excerpt): "...${p.excerpt()}..."')
	}
}

// check_one_of returns true if the current token's `Kind` is equal that of `expected_token`.
fn (mut p Parser) check_one_of(tokens []token.Kind) ? {
	if p.tok.kind in tokens {
		p.next() ?
	} else {
		return error(@MOD + '.' + @STRUCT + '.' + @FN +
			' expected one of $tokens but found "$p.tok.kind" in this (excerpt): "...${p.excerpt()}..."')
	}
}

// is_at returns true if the token kind is equal to `expected_token`.
fn (mut p Parser) is_at(expected_token token.Kind) bool {
	return p.tok.kind == expected_token
}

// expect will error if the token kind is not equal to `expected_token`.
fn (mut p Parser) expect(expected_token token.Kind) ? {
	if p.tok.kind == expected_token {
		return
	} else {
		return error(@MOD + '.' + @STRUCT + '.' + @FN +
			' expected token "$expected_token" but found "$p.tok.kind" in this text "...${p.excerpt()}..."')
	}
}

// find_table returns a reference to a map if found in the *root* table given a "dotted" key (`a.b.c`).
// If some segments of the key does not exist in the root table find_table will
// allocate a new map for each segment. This behavior is needed because you can
// reference maps by multiple keys "dotted" (separated by "." periods) in TOML documents.
// See also `find_in_table`.
pub fn (mut p Parser) find_table() ?&map[string]ast.Value {
	util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'locating "$p.root_map_key" in map ${ptr_str(p.root_map)}')
	mut t := &map[string]ast.Value{}
	unsafe {
		t = &p.root_map
	}
	if p.root_map_key == '' {
		return t
	}

	return p.find_in_table(mut t, p.root_map_key)
}

// sub_table_key returns the logic parts of a dotted key (`a.b.c`) for
// use with the `find_sub_table` method.
pub fn (mut p Parser) sub_table_key(key string) (string, string) {
	mut ks := key.split('.')
	last := ks.last()
	ks.delete_last()
	return ks.join('.'), last
}

// find_sub_table returns a reference to a map if found in the *root* table given a "dotted" key (`a.b.c`).
// If some segments of the key does not exist in the input map find_sub_table will
// allocate a new map for the segment. This behavior is needed because you can
// reference maps by multiple keys "dotted" (separated by "." periods) in TOML documents.
// See also `find_in_table`.
pub fn (mut p Parser) find_sub_table(key string) ?&map[string]ast.Value {
	mut ky := p.root_map_key + '.' + key
	if p.root_map_key == '' {
		ky = key
	}
	util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'locating "$ky" in map ${ptr_str(p.root_map)}')
	mut t := &map[string]ast.Value{}
	unsafe {
		t = &p.root_map
	}
	if ky == '' {
		return t
	}

	return p.find_in_table(mut t, ky)
}

// find_in_table returns a reference to a map if found in `table` given a "dotted" key (`a.b.c`).
// If some segments of the key does not exist in the input map find_in_table will
// allocate a new map for the segment. This behavior is needed because you can
// reference maps by multiple keys "dotted" (separated by "." periods) in TOML documents.
pub fn (mut p Parser) find_in_table(mut table map[string]ast.Value, key string) ?&map[string]ast.Value {
	// NOTE This code is the result of much trial and error.
	// I'm still not quite sure *exactly* why it works. All I can leave here is a hope
	// that this kind of minefield someday will be easier in V :)
	util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'locating "$key" in map ${ptr_str(table)}')
	mut t := &map[string]ast.Value{}
	unsafe {
		t = &table
	}
	ks := key.split('.')
	unsafe {
		for k in ks {
			if k in t.keys() {
				util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'found key "$k" in $t.keys()')
				if val := t[k] or {
					return error(@MOD + '.' + @STRUCT + '.' + @FN +
						' this should never happen. Key "$k" was checked before access')
				}
				{
					if val is map[string]ast.Value {
						// unsafe {
						t = &(t[k] as map[string]ast.Value)
						//}
					} else {
						return error(@MOD + '.' + @STRUCT + '.' + @FN + ' "$k" is not a map')
					}
				}
			} else {
				util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'no key "$k" found, allocating new map "$k" in map ${ptr_str(t)}"')
				// unsafe {
				t[k] = map[string]ast.Value{}
				t = &(t[k] as map[string]ast.Value)
				util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'allocated new map ${ptr_str(t)}"')
				//}
			}
		}
	}
	util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'returning map ${ptr_str(t)}"')
	return t
}

// sub_key parses next tokens as sub/nested keys. This is the also referred to as
// a "dotted" key (`a.b.c`). sub_key returns a string in dotted form.
pub fn (mut p Parser) sub_key() ?string {
	util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'parsing nested key...')
	key := p.key() ?
	mut text := key.str()
	for p.peek_tok.kind == .period {
		p.next() ? // .
		p.check(.period) ?
		next_key := p.key() ?
		text += '.' + next_key.text
	}
	p.next() ?
	util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'parsed nested key `$text` now at "$p.tok.kind" "$p.tok.lit"')
	return text
}

// root_table parses next tokens into the root map of `ast.Value`s.
// The V `map` type is corresponding to a "table" in TOML.
pub fn (mut p Parser) root_table() ? {
	util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'parsing root table...')

	for p.tok.kind != .eof {
		if !p.skip_next {
			p.next() ?
		} else {
			p.skip_next = false
		}

		util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'parsing token "$p.tok.kind" "$p.tok.lit"')
		match p.tok.kind {
			.hash {
				c := p.comment()
				p.ast_root.comments << c
				util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'skipping comment "$c.text"')
			}
			//.whitespace, .tab, .nl {
			//	util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'skipping "$p.tok.kind "$p.tok.lit"')
			//}
			.bare, .quoted, .boolean, .number, .underscore { // NOTE .boolean allows for use of "true" and "false" as table keys
				if p.peek_tok.kind == .assign
					|| (p.tok.kind == .number && p.peek_tok.kind == .minus) {
					key, val := p.key_value() ?

					t := p.find_table() ?
					unsafe {
						util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'setting "$key.str()" = $val.to_json() in table ${ptr_str(t)}')
						t[key.str()] = val
					}
				} else if p.peek_tok.kind == .period {
					subkey := p.sub_key() ?

					p.check(.assign) ?
					val := p.value() ?

					sub_table, key := p.sub_table_key(subkey)

					t := p.find_sub_table(sub_table) ?
					unsafe {
						util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'setting "$key" = $val.to_json() in table ${ptr_str(t)}')
						t[key] = val
					}
				} else {
					return error(@MOD + '.' + @STRUCT + '.' + @FN +
						' dead end at "$p.tok.kind" "$p.tok.lit"')
				}
			}
			.lsbr {
				p.check(.lsbr) ? // '[' bracket

				if p.tok.kind == .lsbr {
					p.array_of_tables(mut &p.root_map) ?
					p.skip_next = true // skip calling p.next() in coming iteration
					util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'leaving double bracket at "$p.tok.kind "$p.tok.lit". NEXT is "$p.peek_tok.kind "$p.peek_tok.lit"')
				} else if p.peek_tok.kind == .period {
					p.root_map_key = p.sub_key() ?
					util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'setting root map key to `$p.root_map_key` at "$p.tok.kind" "$p.tok.lit"')
					p.expect(.rsbr) ?
				} else {
					key := p.key() ?
					p.root_map_key = key.str()
					util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'setting root map key to `$p.root_map_key` at "$p.tok.kind" "$p.tok.lit"')
					p.next() ?
					p.expect(.rsbr) ?
				}
			}
			.eof {
				return
			}
			else {
				return error(@MOD + '.' + @STRUCT + '.' + @FN +
					' could not parse "$p.tok.kind" "$p.tok.lit" in this (excerpt): "...${p.excerpt()}..."')
			}
		}
	}
}

// excerpt returns a string of the characters surrounding `Parser.tok.pos`
fn (p Parser) excerpt() string {
	return p.scanner.excerpt(p.tok.pos, 10)
}

// inline_table parses next tokens into a map of `ast.Value`s.
// The V map type is corresponding to a "table" in TOML.
pub fn (mut p Parser) inline_table(mut tbl map[string]ast.Value) ? {
	util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'parsing inline table into ${ptr_str(tbl)}...')

	mut previous_token_was_value := false
	for p.tok.kind != .eof {
		p.next() ?
		util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'parsing token "$p.tok.kind"')

		if previous_token_was_value {
			if p.tok.kind != .rcbr {
				p.expect(.comma) ?
			}
			previous_token_was_value = false
		}

		match p.tok.kind {
			//.whitespace, .tab, .nl {
			//	util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'skipping "$p.tok.kind "$p.tok.lit"')
			//}
			.comma {
				if p.peek_tok.kind == .rcbr {
					p.next() ? // Forward to the peek_tok
					return error(@MOD + '.' + @STRUCT + '.' + @FN +
						' unexpected "$p.tok.kind" "$p.tok.lit" at this (excerpt): "...${p.excerpt()}..."')
				}
				if p.peek_tok.kind == .comma {
					p.next() ? // Forward to the peek_tok
					return error(@MOD + '.' + @STRUCT + '.' + @FN +
						' unexpected "$p.tok.kind" "$p.tok.lit" at this (excerpt): "...${p.excerpt()}..."')
				}
				util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'skipping comma table value seperator "$p.tok.lit"')
				continue
			}
			.rcbr {
				// '}' bracket
				return
			}
			.bare, .quoted, .boolean, .number, .underscore {
				if p.peek_tok.kind == .assign {
					key, val := p.key_value() ?
					util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'inserting @5 "$key.str()" = $val.to_json() into ${ptr_str(tbl)}')
					tbl[key.str()] = val
				} else if p.peek_tok.kind == .period {
					subkey := p.sub_key() ?
					p.check(.assign) ?
					val := p.value() ?

					sub_table, key := p.sub_table_key(subkey)

					mut t := p.find_in_table(mut tbl, sub_table) ?
					unsafe {
						util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'inserting @6 "$key" = $val.to_json() into ${ptr_str(t)}')
						t[key] = val
					}
				} else {
					return error(@MOD + '.' + @STRUCT + '.' + @FN +
						' dead end at "$p.tok.kind" "$p.tok.lit"')
				}
				previous_token_was_value = true
			}
			else {
				return error(@MOD + '.' + @STRUCT + '.' + @FN +
					' unexpected "$p.tok.kind" "$p.tok.lit" at this (excerpt): "...${p.excerpt()}..."')
			}
		}
	}
	// Make sure the inline-table actually use the return at .rcbr match branch.
	return error(@MOD + '.' + @STRUCT + '.' + @FN +
		' unexpected end of inline-table "$p.tok.kind" "$p.tok.lit" at this (excerpt): "...${p.excerpt()}..."')
}

// array_of_tables parses next tokens into an array of `ast.Value`s.
pub fn (mut p Parser) array_of_tables(mut table map[string]ast.Value) ? {
	util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'parsing array of tables "$p.tok.kind" "$p.tok.lit"')
	// NOTE this is starting to get ugly. TOML isn't simple at this point
	p.check(.lsbr) ? // '[' bracket

	// [[key.key]] horror
	if p.peek_tok.kind == .period {
		p.double_array_of_tables(mut table) ?
		return
	}

	key := p.key() ?
	p.next() ?
	p.check(.rsbr) ?
	p.check(.rsbr) ?

	key_str := key.str()
	unsafe {
		if key_str in table.keys() {
			if val := table[key_str] or {
				return error(@MOD + '.' + @STRUCT + '.' + @FN +
					' this should never happen. Key "$key_str" was checked before access')
			}
			{
				if val is []ast.Value {
					arr := &(table[key_str] as []ast.Value)
					arr << p.double_bracket_array() ?
					table[key_str] = arr
				} else {
					return error(@MOD + '.' + @STRUCT + '.' + @FN +
						' table[$key_str] is not an array. (excerpt): "...${p.excerpt()}..."')
				}
			}
		} else {
			table[key_str] = p.double_bracket_array() ?
		}
	}
	p.last_aot = key_str
	p.last_aot_index = 0
}

// double_array_of_tables parses next tokens into an array of tables of arrays of `ast.Value`s...
pub fn (mut p Parser) double_array_of_tables(mut table map[string]ast.Value) ? {
	util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'parsing array of tables of arrays "$p.tok.kind" "$p.tok.lit"')

	key := p.key() ?
	mut key_str := key.str()
	for p.peek_tok.kind == .period {
		p.next() ? // .
		p.check(.period) ?
		next_key := p.key() ?
		key_str += '.' + next_key.text
	}

	p.next() ?
	p.check(.rsbr) ?
	p.check(.rsbr) ?

	ks := key_str.split('.')

	if ks.len != 2 {
		return error(@MOD + '.' + @STRUCT + '.' + @FN +
			' nested array of tables does not support more than 2 levels. (excerpt): "...${p.excerpt()}..."')
	}

	first := ks[0]
	last := ks[1]

	unsafe {
		// NOTE this is starting to get EVEN uglier. TOML is not at all simple at this point...
		if p.last_aot != first {
			table[first] = []ast.Value{}
			p.last_aot = first
			mut t_arr := &(table[p.last_aot] as []ast.Value)
			t_arr << map[string]ast.Value{}
			p.last_aot_index = 0
		}

		mut t_arr := &(table[p.last_aot] as []ast.Value)
		mut t_map := t_arr[p.last_aot_index]
		mut t := &(t_map as map[string]ast.Value)

		if last in t.keys() {
			if val := t[last] or {
				return error(@MOD + '.' + @STRUCT + '.' + @FN +
					' this should never happen. Key "$last" was checked before access')
			}
			{
				if val is []ast.Value {
					arr := &(val as []ast.Value)
					arr << p.double_bracket_array() ?
					t[last] = arr
				} else {
					return error(@MOD + '.' + @STRUCT + '.' + @FN +
						' t[$last] is not an array. (excerpt): "...${p.excerpt()}..."')
				}
			}
		} else {
			t[last] = p.double_bracket_array() ?
		}
	}
}

// array parses next tokens into an array of `ast.Value`s.
pub fn (mut p Parser) double_bracket_array() ?[]ast.Value {
	mut arr := []ast.Value{}
	for p.tok.kind in [.bare, .quoted, .boolean, .number] && p.peek_tok.kind == .assign {
		mut tbl := map[string]ast.Value{}
		key, val := p.key_value() ?
		tbl[key.str()] = val
		arr << tbl
		p.next() ?
	}
	return arr
}

// array parses next tokens into an array of `ast.Value`s.
pub fn (mut p Parser) array() ?[]ast.Value {
	util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'parsing array...')
	mut arr := []ast.Value{}
	p.expect(.lsbr) ? // '[' bracket
	mut previous_token_was_value := false
	for p.tok.kind != .eof {
		p.next() ?
		util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'parsing token "$p.tok.kind" "$p.tok.lit"')

		if previous_token_was_value {
			if p.tok.kind != .rsbr && p.tok.kind != .hash {
				p.expect(.comma) ?
			}
			previous_token_was_value = false
		}

		match p.tok.kind {
			.boolean {
				arr << ast.Value(p.boolean() ?)
				previous_token_was_value = true
			}
			.comma {
				// Trailing commas before array close is allowed
				// so we skip `if p.peek_tok.kind == .rsbr { ... }`
				if p.peek_tok.kind == .comma {
					p.next() ? // Forward to the peek_tok
					return error(@MOD + '.' + @STRUCT + '.' + @FN +
						' unexpected "$p.tok.kind" "$p.tok.lit" at this (excerpt): "...${p.excerpt()}..."')
				}
				util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'skipping comma table value seperator "$p.tok.lit"')
				continue
			}
			.eof {
				return error(@MOD + '.' + @STRUCT + '.' + @FN +
					' could not parse array. Reached EOF "$p.tok.kind" "$p.tok.lit" ("$p.tok.lit") in this (excerpt): "...${p.excerpt()}..."')
			}
			.hash {
				c := p.comment()
				p.ast_root.comments << c
				util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'skipping comment "$c.text"')
			}
			.lcbr {
				mut t := map[string]ast.Value{}
				p.inline_table(mut t) ?
				arr << ast.Value(t)
				previous_token_was_value = true
			}
			.number {
				val := p.number_or_date() ?
				arr << val
				previous_token_was_value = true
			}
			.quoted {
				arr << ast.Value(p.quoted())
				previous_token_was_value = true
			}
			.lsbr {
				util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'parsing array in array "$p.tok.kind" "$p.tok.lit"')
				arr << ast.Value(p.array() ?)
				previous_token_was_value = true
			}
			.rsbr {
				break
			}
			else {
				error(@MOD + '.' + @STRUCT + '.' + @FN +
					' could not parse  "$p.tok.kind" "$p.tok.lit" ("$p.tok.lit") in this (excerpt): "...${p.excerpt()}..."')
			}
		}
	}
	p.expect(.rsbr) ? // ']' bracket
	$if debug {
		flat := arr.str().replace('\n', r'\n')
		util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'parsed array: $flat . Currently @ token "$p.tok.kind"')
	}
	return arr
}

// comment returns an `ast.Comment` type.
pub fn (mut p Parser) comment() ast.Comment {
	util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'parsed hash comment "#$p.tok.lit"')
	return ast.Comment{
		text: p.tok.lit
		pos: p.tok.position()
	}
}

// key parse and returns an `ast.Key` type.
// Keys are the token(s) appearing before an assignment operator (=).
pub fn (mut p Parser) key() ?ast.Key {
	util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'parsing key from "$p.tok.lit" ...')

	mut key := ast.Key(ast.Null{})
	if p.tok.kind == .number {
		if p.peek_tok.kind == .minus {
			mut lits := p.tok.lit
			pos := p.tok.position()
			for p.peek_tok.kind != .assign {
				p.next() ?
				lits += p.tok.lit
			}
			return ast.Key(ast.Bare{
				text: lits
				pos: pos
			})
		}
		// number := p.number() as ast.Number
		key = ast.Key(p.number())
	} else {
		key = match p.tok.kind {
			.bare, .underscore {
				ast.Key(p.bare())
			}
			.boolean {
				ast.Key(p.boolean() ?)
			}
			.quoted {
				ast.Key(p.quoted())
			}
			else {
				error(@MOD + '.' + @STRUCT + '.' + @FN +
					' key expected .bare, .number, .quoted or .boolean but got "$p.tok.kind"')
				ast.Key(ast.Bare{}) // TODO workaround bug
			}
		}
	}

	// NOTE kept for eased debugging
	// util.printdbg(@MOD +'.' + @STRUCT + '.' + @FN, 'parsed key "$p.tok.lit"')
	// panic(@MOD + '.' + @STRUCT + '.' + @FN + ' could not parse ${p.tok.kind} ("${p.tok.lit}") token \n$p.tok')
	// return ast.Key(ast.Bare{})

	return key
}

// key_value parse and returns a pair `ast.Key` and `ast.Value` type.
// see also `key()` and `value()`
pub fn (mut p Parser) key_value() ?(ast.Key, ast.Value) {
	util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'parsing key value pair...')
	key := p.key() ?
	p.next() ?
	p.check(.assign) ? // Assignment operator
	value := p.value() ?
	util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'parsed key value pair. "$key" = $value.to_json()')
	return key, value
}

// value parse and returns an `ast.Value` type.
// values are the token(s) appearing after an assignment operator (=).
pub fn (mut p Parser) value() ?ast.Value {
	util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'parsing value...')
	// println('parsed comment "${p.tok.lit}"')

	mut value := ast.Value(ast.Null{})

	util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'parsing token "$p.tok.kind" "$p.tok.lit"')
	// mut value := ast.Value{}
	if p.tok.kind == .number {
		number_or_date := p.number_or_date() ?
		value = number_or_date
	} else {
		value = match p.tok.kind {
			.quoted {
				ast.Value(p.quoted())
			}
			.boolean {
				ast.Value(p.boolean() ?)
			}
			.lsbr {
				ast.Value(p.array() ?)
			}
			.lcbr {
				mut t := map[string]ast.Value{}
				p.inline_table(mut t) ?
				// table[key_str] = ast.Value(t)
				ast.Value(t)
			}
			else {
				ast.Value(ast.Null{})
			}
		}
		if value is ast.Null {
			return error(@MOD + '.' + @STRUCT + '.' + @FN +
				' value expected .boolean, .quoted, .lsbr, .lcbr or .number got "$p.tok.kind" "$p.tok.lit"')
		}
	}
	util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'parsed "$p.tok.kind" as value $value.to_json()')
	return value
}

// number_or_date parse and returns an `ast.Value` type as
// one of [`ast.Date`, `ast.Time`, `ast.DateTime`, `ast.Number`]
pub fn (mut p Parser) number_or_date() ?ast.Value {
	// Handle Date/Time
	if p.peek_tok.kind == .minus || p.peek_tok.kind == .colon {
		date_time_type := p.date_time() ?
		match date_time_type {
			ast.Date {
				return ast.Value(date_time_type as ast.Date)
			}
			ast.Time {
				return ast.Value(date_time_type as ast.Time)
			}
			ast.DateTime {
				return ast.Value(date_time_type as ast.DateTime)
			}
		}
	}
	return ast.Value(p.number())
}

// bare parse and returns an `ast.Bare` type.
pub fn (mut p Parser) bare() ast.Bare {
	return ast.Bare{
		text: p.tok.lit
		pos: p.tok.position()
	}
}

// quoted parse and returns an `ast.Quoted` type.
pub fn (mut p Parser) quoted() ast.Quoted {
	// To get more info about the quote type and enable better checking,
	// the scanner is returning the literal *with* single- or double-quotes.
	mut quote := p.tok.lit[0]
	is_multiline := p.tok.lit.len >= 6 && p.tok.lit[1] == quote && p.tok.lit[2] == quote
	mut lit := p.tok.lit[1..p.tok.lit.len - 1]
	if is_multiline {
		lit = p.tok.lit[3..p.tok.lit.len - 3]
	}
	return ast.Quoted{
		text: lit
		pos: p.tok.position()
		quote: quote
		is_multiline: is_multiline
	}
}

// boolean parse and returns an `ast.Bool` type.
pub fn (mut p Parser) boolean() ?ast.Bool {
	if p.tok.lit !in ['true', 'false'] {
		return error(@MOD + '.' + @STRUCT + '.' + @FN +
			' expected literal to be either `true` or `false` got "$p.tok.kind"')
	}
	return ast.Bool{
		text: p.tok.lit
		pos: p.tok.position()
	}
}

// number parse and returns an `ast.Number` type.
pub fn (mut p Parser) number() ast.Number {
	return ast.Number{
		text: p.tok.lit
		pos: p.tok.position()
	}
}

// date_time parses dates and time in RFC 3339 format.
// https://datatracker.ietf.org/doc/html/rfc3339
pub fn (mut p Parser) date_time() ?ast.DateTimeType {
	// Date and/or Time
	mut lit := ''
	pos := p.tok.position()
	mut date := ast.Date{}
	mut time := ast.Time{}

	if p.peek_tok.kind == .minus {
		date = p.date() ?
		lit += date.text
		// Look for any THH:MM:SS or <space>HH:MM:SS
		if (p.peek_tok.kind == .bare && (p.peek_tok.lit.starts_with('T')
			|| p.peek_tok.lit.starts_with('t'))) || p.peek_tok.kind == .whitespace {
			p.next() ? // Advance to token with Txx or whitespace special case
			if p.tok.lit.starts_with('T') || p.tok.lit.starts_with('t') {
				lit += p.tok.lit[0].ascii_str() //'T' or 't'
			} else {
				lit += p.tok.lit
				p.next() ?
			}
			time = p.time() ?
			lit += time.text

			util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'parsed date-time: "$lit"')
			return ast.DateTime{
				text: lit
				pos: pos
				date: date
				time: time
			}
		}
	} else if p.peek_tok.kind == .colon {
		time = p.time() ?
		return time
	}

	return ast.Date{
		text: lit
		pos: pos
	}
}

// date parse and returns an `ast.Date` type.
pub fn (mut p Parser) date() ?ast.Date {
	// Date
	mut lit := p.tok.lit
	pos := p.tok.position()

	p.check(.number) ?
	lit += p.tok.lit
	p.check(.minus) ?
	lit += p.tok.lit
	p.check(.number) ?
	lit += p.tok.lit
	p.check(.minus) ?
	lit += p.tok.lit
	p.expect(.number) ?

	util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'parsed date: "$lit"')
	return ast.Date{
		text: lit
		pos: pos
	}
}

// time parse and returns an `ast.Time` type.
pub fn (mut p Parser) time() ?ast.Time {
	// Time
	mut lit := p.tok.lit
	pos := p.tok.position()

	if p.is_at(.bare) && (lit.starts_with('T') || lit.starts_with('t')) {
		if p.tok.lit.starts_with('T') {
			lit = lit.all_after('T')
		} else if p.tok.lit.starts_with('t') {
			lit = lit.all_after('t')
		}
		p.next() ?
	} else {
		p.check(.number) ?
	}
	lit += p.tok.lit
	p.check(.colon) ?
	lit += p.tok.lit
	p.check(.number) ?
	lit += p.tok.lit
	// TODO does TOML even have optional seconds?
	// if p.peek_tok.kind == .colon {
	p.check(.colon) ?
	lit += p.tok.lit
	p.expect(.number) ?
	//}

	// Optional milliseconds
	if p.peek_tok.kind == .period {
		p.next() ?
		lit += p.tok.lit // lit += '.'
		p.check(.period) ?
		lit += p.tok.lit
		p.expect(.number) ?
	}

	// Parse offset
	if p.peek_tok.kind == .minus || p.peek_tok.kind == .plus {
		p.next() ?
		lit += p.tok.lit // lit += '-'
		p.check_one_of([.minus, .plus]) ?
		lit += p.tok.lit
		p.check(.number) ?
		lit += p.tok.lit
		p.check(.colon) ?
		lit += p.tok.lit
		p.expect(.number) ?
	} else if p.peek_tok.kind == .bare && (p.peek_tok.lit == 'Z' || p.peek_tok.lit == 'z') {
		p.next() ?
		lit += p.tok.lit
		p.expect(.bare) ?
	}

	util.printdbg(@MOD + '.' + @STRUCT + '.' + @FN, 'parsed time: "$lit"')
	return ast.Time{
		text: lit
		pos: pos
	}
}

// eof returns an `ast.EOF` type.
pub fn (mut p Parser) eof() ast.EOF {
	return ast.EOF{
		pos: p.tok.position()
	}
}