import {
	App,
	Editor,
	EditorChange,
	EditorPosition,
	EditorRange,
	EditorRangeOrCaret,
	EditorSelection,
	EditorTransaction,
	MarkdownFileInfo,
	MarkdownView,
} from 'obsidian'
import BindThemPlugin from './main'
import { getMainSelection, selectionToRange } from './Utils'
import { PRE_WIDOW_EXPAND_CHARS, POST_WIDOW_EXPAND_CHARS } from './Constants'

/**
 * BetterFormatting provides enhanced markdown formatting toggling
 * that intelligently expands selections to word boundaries and
 * handles widow characters.
 */
export class BetterFormatting {
	public app: App
	private plugin: BindThemPlugin

	constructor(app: App, plugin: BindThemPlugin) {
		this.app = app
		this.plugin = plugin
	}

	/**
	 * Expand a range by words, including intelligent handling of widow characters
	 */
	private expandRangeByWords(
		editor: Editor,
		range: EditorRange,
		symbolStart: string,
		symbolEnd: string
	): EditorRange {
		// Expand to word boundaries
		let from = (editor.wordAt(range.from) || range).from
		let to = (editor.wordAt(range.to) || range).to

		// Include leading 'widows' (characters that should be included before the word)
		while (true) {
			const newFrom: EditorPosition = {
				line: from.line,
				ch: from.ch - 1,
			}

			const newTo: EditorPosition = {
				line: to.line,
				ch: to.ch + 1,
			}

			const preChar = editor.getRange(newFrom, from)
			const postChar = editor.getRange(to, newTo)

			// Don't do this if widows form a matched pair
			if (preChar === postChar) {
				break
			}

			if (symbolStart.endsWith(preChar)) {
				break
			}

			if (!PRE_WIDOW_EXPAND_CHARS.includes(preChar)) {
				break
			}

			from = newFrom
		}

		// Include trailing 'widows'
		while (true) {
			const newFrom: EditorPosition = {
				line: from.line,
				ch: from.ch - 1,
			}

			const newTo: EditorPosition = {
				line: to.line,
				ch: to.ch + 1,
			}

			const preChar = editor.getRange(newFrom, from)
			const postChar = editor.getRange(to, newTo)

			// Don't do this if widows form a matched pair
			if (preChar === postChar) {
				break
			}

			if (symbolEnd.startsWith(postChar)) {
				break
			}

			if (!POST_WIDOW_EXPAND_CHARS.includes(postChar)) {
				break
			}

			to = newTo
		}

		// Include leading symbolStart
		const newFrom = { line: from.line, ch: from.ch - symbolStart.length }
		const preString = editor.getRange(newFrom, from)
		if (preString === symbolStart) {
			from = newFrom
		}

		// Include following symbolEnd
		const newTo = { line: to.line, ch: to.ch + symbolEnd.length }
		const postString = editor.getRange(to, newTo)
		if (postString === symbolEnd) {
			to = newTo
		}

		return {
			from: from,
			to: to,
		}
	}

	/**
	 * Check if text in the given range is already wrapped with the specified symbols
	 */
	private isWrapped(
		editor: Editor,
		range: EditorRange,
		symbolStart: string,
		symbolEnd: string
	): boolean {
		const text = editor.getRange(range.from, range.to)
		return text.startsWith(symbolStart) && text.endsWith(symbolEnd)
	}

	/**
	 * Create changes to wrap text with symbols
	 */
	private wrap(
		editor: Editor,
		textRange: EditorRange,
		selection: EditorSelection,
		symbolStart: string,
		symbolEnd: string
	): [Array<EditorChange>, EditorSelection] {
		const changes: Array<EditorChange> = [
			{
				from: textRange.from,
				text: symbolStart,
			},
			{
				from: textRange.to,
				text: symbolEnd,
			},
		]

		const newSelection: EditorSelection = {
			anchor: { ...selection.anchor },
			head: { ...selection.head },
		}
		newSelection.anchor.ch += symbolStart.length
		newSelection.head.ch += symbolEnd.length

		return [changes, newSelection]
	}

	/**
	 * Create changes to unwrap text from symbols
	 */
	private unwrap(
		editor: Editor,
		textRange: EditorRange,
		selection: EditorSelection,
		symbolStart: string,
		symbolEnd: string
	): [Array<EditorChange>, EditorSelection] {
		const changes: Array<EditorChange> = [
			{
				from: textRange.from,
				to: {
					line: textRange.from.line,
					ch: textRange.from.ch + symbolStart.length,
				},
				text: '',
			},
			{
				from: {
					line: textRange.to.line,
					ch: textRange.to.ch - symbolEnd.length,
				},
				to: textRange.to,
				text: '',
			},
		]

		const newSelection: EditorSelection = {
			anchor: { ...selection.anchor },
			head: { ...selection.head },
		}
		newSelection.anchor.ch -= symbolStart.length
		newSelection.head.ch -= symbolStart.length

		return [changes, newSelection]
	}

	/**
	 * Set the wrap state for a selection
	 */
	private setSelectionWrapState(
		editor: Editor,
		selection: EditorSelection,
		wrapState: boolean,
		symbolStart: string,
		symbolEnd: string
	): [Array<EditorChange>, EditorSelection] {
		const initialRange = selectionToRange(selection)
		const textRange: EditorRange = this.expandRangeByWords(
			editor,
			initialRange,
			symbolStart,
			symbolEnd
		)

		// Check if already wrapped
		const alreadyWrapped = this.isWrapped(editor, textRange, symbolStart, symbolEnd)
		if (alreadyWrapped === wrapState) {
			return [[], selection]
		}

		// Wrap or unwrap
		if (wrapState) {
			return this.wrap(editor, textRange, selection, symbolStart, symbolEnd)
		}

		return this.unwrap(editor, textRange, selection, symbolStart, symbolEnd)
	}

	/**
	 * Toggle wrapper symbols around the current selection(s)
	 * 
	 * Principle: Toggling twice == no-op
	 */
	public toggleWrapper(
		editor: Editor,
		view: MarkdownView | MarkdownFileInfo,
		symbolStart: string,
		symbolEnd?: string
	): void {
		if (symbolEnd === undefined) {
			symbolEnd = symbolStart
		}

		const selections = editor.listSelections()
		const mainSelection = getMainSelection(editor)

		// Get wrapped state of main selection
		const mainRange: EditorRange = this.expandRangeByWords(
			editor,
			selectionToRange(mainSelection),
			symbolStart,
			symbolEnd
		)

		// Check if already wrapped
		const isWrapped = this.isWrapped(editor, mainRange, symbolStart, symbolEnd)
		const targetWrapState = !isWrapped

		// Process all selections
		const newChanges: Array<EditorChange> = []
		const newSelectionRanges: Array<EditorRangeOrCaret> = []

		for (const selection of selections) {
			const [changes, newSelection] = this.setSelectionWrapState(
				editor,
				selection,
				targetWrapState,
				symbolStart,
				symbolEnd
			)

			newChanges.push(...changes)
			newSelectionRanges.push(selectionToRange(newSelection))
		}

		const transaction: EditorTransaction = {
			changes: newChanges,
			selections: newSelectionRanges,
		}

		let origin = targetWrapState ? '+' : '-'
		origin += 'BetterFormatting_' + symbolStart + symbolEnd

		editor.transaction(transaction, origin)
	}
}