import { JexlEngineProvider } from './jexl-engine-provider';

interface MiddleExpression {
    expression: any;
    nextText?: string;
}

export class ExpressionCompiler {

    private ESCAPE_CHAR = '\\';
    private SPECIAL_CHAR = '$';
    private BRACKET_BEGIN = '{';
    private BRACKET_END = '}';

    jexlEngineProvider: JexlEngineProvider;

    compileSections(text: string): any[] {
        if (!text || text.indexOf(this.SPECIAL_CHAR) < 0) {
            return [];
        }

        const sections: any[] = [];
        let middleText: string | undefined = text;
        while (middleText) {
            const me: MiddleExpression | undefined = this.middleCompile(middleText);
            if (!me) {
                sections.push(middleText);
                middleText = undefined;
            } else {
                sections.push(me.expression);
                middleText = me.nextText;
            }
        }

        return sections;
    }

    protected middleCompile(text: string): MiddleExpression | undefined {
        let me: MiddleExpression | undefined;
        if (text.startsWith('${{')) {
            me = this.nextString(text); // runtime expression
        } else if (text.startsWith('${')) {
            me = this.nextMiddleExpression(text.substring(2));
        } else {
            me = this.nextString(text);
        }
        return me;
    }

    protected nextMiddleExpression(text: string): MiddleExpression | undefined {
        let stringed = false;
        let escaped = false;
        let bracketBeginCharFound = 0;

        const section: string[] = [];
        for (let i = 0; i < text.length; i++) {
            const c = text[i];
            if (!escaped) {
                if ('\'' === c || '"' === c) {
                    stringed = !stringed;
                    section.push(c);
                    continue;
                } else
                    if (c === this.ESCAPE_CHAR) {
                        escaped = true;
                        continue;
                    }
            }

            if (stringed) {
                section.push(c);
                escaped = false;
            } else if (escaped) {
                if (this.SPECIAL_CHAR === c || this.BRACKET_BEGIN === c || this.BRACKET_END === c) {
                    section.push(c);
                } else {
                    section.push(this.ESCAPE_CHAR);
                    section.push(c);
                }
                escaped = false;
            } else if (this.BRACKET_BEGIN === c) {
                bracketBeginCharFound++;
                section.push(c);
            } else if (this.BRACKET_END === c) {
                if (bracketBeginCharFound === 0) {
                    const jexlEngine = this.jexlEngineProvider.provide();
                    const expression = jexlEngine.createExpression(section.join(''));
                    let nextText;
                    if (i !== text.length - 1) {
                        nextText = text.substring(i + 1);
                    }
                    return { expression, nextText };
                } else {
                    bracketBeginCharFound--;
                    section.push(c);
                }
            } else {
                section.push(c);
            }
        }
    }

    protected nextString(text: string): MiddleExpression {
        let escaped = false;
        let specialCharFound = false;

        const section: string[] = [];
        for (let i = 0; i < text.length; i++) {
            const c = text[i];
            if (!escaped) {
                if ('\'' === c || '"' === c) {
                    section.push(c);
                    continue;
                } else
                    if (c === this.ESCAPE_CHAR) {
                        escaped = true;
                        continue;
                    }
            }

            if (escaped) {
                if (this.SPECIAL_CHAR === c || this.BRACKET_BEGIN === c || this.BRACKET_END === c) {
                    section.push(c);
                } else {
                    section.push(this.ESCAPE_CHAR);
                    section.push(c);
                }
                escaped = false;
            } else
                if (specialCharFound) {
                    if (this.BRACKET_BEGIN === c) {
                        const expression = section.join('');
                        const nextText = text.substring(i - 1);
                        return { expression, nextText };
                    } else {
                        specialCharFound = false;
                        section.push(this.SPECIAL_CHAR);
                        section.push(c);
                    }
                } else {
                    if (this.SPECIAL_CHAR === c && text.length > i + 2
                        && text[i + 1] === this.BRACKET_BEGIN && text[i + 2] !== this.BRACKET_BEGIN) {
                        specialCharFound = true;
                    } else {
                        section.push(c);
                    }
                }
        }

        return { expression: section.join('') };
    }

}