import { CompletionContext, CompletionResult } from '@codemirror/autocomplete'
import type { EditorState } from '@codemirror/state'

const NUNJUCKS_KEYWORDS = [
    'if', 'endif', 'elif', 'else', 'for', 'endfor', 'in', 'and', 'or', 'not',
    'true', 'false', 'none', 'macro', 'endmacro', 'set', 'endset', 'block', 'endblock',
    'extends', 'include', 'import', 'with', 'endwith', 'filter', 'endfilter', 'raw', 'endraw',
]

const NUNJUCKS_FILTERS = [
    'default', 'length', 'upper', 'lower', 'title', 'trim', 'join', 'replace',
    'first', 'last', 'round', 'int', 'float', 'string', 'list', 'sort', 'groupby',
    'trim', 'escape', 'safe', 'striptags', 'capitalize', 'reverse', 'batch', 'slice',
]

/** Get line text (CodeMirror 6: doc.line(n) is 1-based) */
function getLineText(state: EditorState, lineNo0Based: number): string {
    return state.doc.line(lineNo0Based + 1).text
}

/** Detect if position is inside {{ or {% from the start of the line */
function insideNunjucks(state: EditorState, lineNo0Based: number, posInLine: number): boolean {
    const line = getLineText(state, lineNo0Based)
    const before = line.slice(0, posInLine)
    const openVar = before.lastIndexOf('{{')
    const openTag = before.lastIndexOf('{%')
    const closeVar = before.lastIndexOf('}}')
    const closeTag = before.lastIndexOf('%}')
    if (openVar > -1 && (closeVar === -1 || closeVar < openVar)) return true
    if (openTag > -1 && (closeTag === -1 || closeTag < openTag)) return true
    return false
}

/** Get the word fragment before the cursor for matching */
function wordBefore(state: EditorState, lineNo0Based: number, posInLine: number): string {
    const line = getLineText(state, lineNo0Based)
    let start = posInLine
    while (start > 0 && /[\w.-]/.test(line[start - 1])) start -= 1
    return line.slice(start, posInLine)
}

export function nunjucksCompletionSource(
    variableIds: string[],
    configTitles?: string[],
    functionIds?: string[],
): (context: CompletionContext) => CompletionResult | null {
    return (context: CompletionContext) => {
        const { state, pos } = context
        const line = state.doc.lineAt(pos)
        if (!insideNunjucks(state, line.number - 1, pos - line.from)) return null

        const word = wordBefore(state, line.number - 1, pos - line.from)
        const from = pos - word.length

        const options: { label: string; type?: string; info?: string }[] = []

        for (const id of variableIds) {
            if (!word || id.toLowerCase().startsWith(word.toLowerCase())) {
                options.push({ label: id, type: 'variable', info: 'Variable' })
            }
        }
        for (const id of functionIds ?? []) {
            if (!word || id.toLowerCase().startsWith(word.toLowerCase())) {
                options.push({ label: id, type: 'function', info: "Filter: {{ '' | " + id + " }}" })
            }
        }
        for (const kw of NUNJUCKS_KEYWORDS) {
            if (!word || kw.startsWith(word.toLowerCase())) {
                options.push({ label: kw, type: 'keyword', info: 'Nunjucks keyword' })
            }
        }
        for (const f of NUNJUCKS_FILTERS) {
            if (!word || f.startsWith(word.toLowerCase())) {
                options.push({ label: `${f}`, type: 'function', info: `Filter: ${f}` })
            }
        }
        if (configTitles?.length) {
            for (const t of configTitles) {
                if (!word || t.toLowerCase().startsWith(word.toLowerCase())) {
                    options.push({ label: t, type: 'variable', info: 'Config' })
                }
            }
        }

        if (options.length === 0) return null
        return {
            from,
            options: options.slice(0, 50),
            validFor: /^[\w.-]*$/,
        }
    }
}